A following method has been known as a method for forming a piezoelectric resonator element by processing a quartz substrate as a piezoelectric material. Such a method has been know, that a quartz resonator as the piezoelectric resonator element is processed by reactive ion etching as dry etching (for example, see Patent Document 1). The dry etching enables a processing that is less affected by anisotropy of the quartz substrate.
[Patent Document 1] JP-A-8-242134 (Page 3, Paragraphs [0020] to [0022])